The most common form of cystic fibrosis (CF) (delta F508) results from loss of functional protein interactions between the cystic fibrosis transmembrane conductance regulator (CFTR) and proteins that are necessary for the normal trafficking of CFTR from the endoplasmic reticulum (ER) to the cell surface. Completion of the human genome project provides a unique opportunity to identify the key protein interactions associated with CFTR transport and function. Although more than 1000 mutations have been identified in the CFTR gene, nearly 70% of patients are homozygous for the delta F508 mutation, which leads to severe forms of CF. Deletion of Phe 508 prevents proper folding and trafficking of CFTR from the endoplasmic reticulum (ER), the first step in the exocytic pathway, to the cell surface. We hypothesize that the Phe 508 deletion results in the loss of key protein interactions necessary to stabilize the maturing protein for export from the ER and functional stabilization at the cell surface. In order to rationally develop therapeutic means to correct the CFTR deficiency at the cell surface, it is critical to understand all the protein interactions governing CFTR function and membrane transport. This proposal will develop and apply the methods of quantitative multi-dimensional protein identification technology (MudPIT) and Multiple Ion Reaction Monitoring (MRM) mass spectrometry to define the protein interactions involved in export of CFTR to and maintenance at the cell surface that are lost in the homozygous delta F508 CFTR mutant. An understanding of the global protein interactions dictating the folding and function of CFTR will significantly advance the CF field by providing a comprehensive catalog of protein interactions in divergent tissues for future studies by the CF community. These studies are anticipated to provide critical insight for identification of novel drugs that will alleviate suffering of individuals afflicted with CF.